iperf is a plugin, not built-in. Then you need to connect to a public iperf server. https://iperf.fr/iperf-servers.php.Or you can just use speedtest.net from a local workstation.

It is a plugin integrated in the OPNsense GUI (not sure if it's installed by default) and called in server mode, I'm not aware how you can connect from the GUI in client mode with the public iperf servers.

Yeah, not pre-installed. Have to install the plugin.Not sure how useful iperf would be if you can't run it as a client. I imagine you would need to install a client somewhere else to talk to. I have not used iperf with OPNsense.

It's pretty useful as it is, at least for me, although a client mode is also welcomed at a point. iperf was the reason I changed my hardware and discovered (i mean not just read about it) OPNsense.

1. First and most important reason to use iperf in server mode is you can test your (or others) WIFI coverage/bandwidth, for real, and plan your setup according to the iperf results. You don't measure this otherwise, unless you want to map the location.2. You get to saturate your LAN (cable) connections and thus you can find your bottlenecks or faulty/misconfigured nodes/devices/clients in your LAN. Speedtest.net usually comes after (if you want accuracy).3. You can accurately verify your ISP if you have access to a proper client (perhaps a friend somewhere with a better link). Of course, you need to know both links (at least theoretical) specifications.4. With iperf, you can test both directions simultaneously.5. Multiple threads...

Iperf is in many ways 1000x more powerful and useful for accurate tests and debugging than speedtest.net and i cannot be more grateful that the awesome guys at OPNsense implemented it.The only thing its missing is a good ping/jitter test, but there are other specialized tools for this.

1. If you have a gigabit lan, test the lan speed2. If you don't get around ~940Mbit/s bandwidth with iperf, it might be a sign something is wrong:- these speeds require raw cpu power, but if you have a powerful cpu, not something to worry about (both client and server)- next, and most common issue with windows systems is the default tcp window size; you can tweak tcp settings with this awesome tool: https://www.speedguide.net/downloads.php; just load the optimal settings, save & reboot- if still performance is low, you might consider upgrading your bios and drivers- if still having issues, you can test your system for dpc latency causing drivers/services and try to tweak them (http://www.resplendence.com/latencymon), as they influence your iperf perfomance3. If you have issues with your lan tests, speedtest.net performance will always be subpar, and iperf, even in your case, is an excellent tool to stress your network and system for errors